With the increased use of plastic components in automobile manufacturing instead of metal components, manufacturing cycle time has decreased even as component configurations have become more intricate. Plastic components can be surface finished to resemble the metal components they replace while reducing weight, reducing waste, and containing manufacturing cost. For example, automotive lamp assemblies once constructed of glass and metal with inherent problems of sealing the metal to glass interface can now be constructed of plastic with weather tight seal.
Typically, a lamp assembly includes a lamp housing and a lens that is secured to the lamp housing by an adhesive or by a seal bead. Older lamp assemblies had the lens secured to the housing by an adhesive. While adhesives worked to provide a seal, they had the disadvantage of requiring time to cure which increased manufacturing time, thereby increasing cost. Adhesive applied before components are assembled also poses a glue squeeze out problem requiring time for clean up. U.S. Pat. No. 5,670,109 which issued Sep. 23, 1997 to DeRees remedied the glue squeeze out problem in some applications by low pressure injection of the adhesive. Recently, the adhesive has been displaced by a seal bead formed of a thermoplastic material introduced during the injection molding process which fastens the lens to the housing without increasing cycle time.
U.S. Pat. No. 5,413,743, which issued May 9, 1995, to P. A. Prophet discloses a lamp assembly that has a plastic housing and plastic lens molded in a rotary transfer molding machine. The rotary transfer molding machine has upper and lower mateable housing dies and upper and lower mateable lens dies in which the housing and the lens are molded simultaneously. The machine is then indexed so that the upper housing die with the molded housing retained in it is mated with the lower lens die with the molding lens retained in it. These two dies are configured so that an annular seal bead cavity is formed at an interface of the dies. A seal bead is then molded to join the molded housing to the molded lens to provide the lamp assembly. The machine is indexed again so that the upper housing die with the lamp assembly retained in it is mated with an overlay die and a decorative overlay is molded on the peripheral margin of the lens. The lens is attached to the housing by an annular seal bead that joins the perimeter of the lens to a peripheral flange at an opening of the lamp housing.
A problem with the rotary transfer molding process is that it requires a rotary transfer molding machine, and it requires that both members to be joined be formed at the same time. Manufacturing both members to be joined in a single machine at the same time may not result in the lowest cost for each component, and may increase machinery complexity. Accordingly, it is desirable to have a process for joining two components regardless of when or where the components were formed.
In the rotary transfer molding machine, the dies are configured so that a seal bead cavity is formed at the interface where the two dies are mated. The seal bead is then molded, joining the molded housing to the molded lens at the interface of the dies to provide the lamp assembly. The dies of the rotary transfer molding machine are required to provide support for the housing and lens while the bead is being formed. Because the two components to be joined are always retained in the rotary transfer molding machine, there is little difficulty with manufacturing tolerances; however, retaining the components to be joined in the machine at all times until the lamp assembly is fully assembled, does not allow for modification or processing of the interior surfaces of the lamp assembly prior to sealing. Accordingly, it will be appreciated that it would be highly desirable to manufacture a lamp assembly without having to invest in machinery of this cost and complexity. It is also desirable to have a joint that is versatile enough to compensate for manufacturing tolerances and which is rigid enough to form the joint without collapsing.